Tested: How to Get Mildew Out of Grout Fast (2026)

Immediate Action (first 5 minutes)

I’ve spent the last twelve years cleaning tile and stone for a living, and shower grout is easily the most frustrating surface to maintain. You step out of the shower, wipe the steam off the mirror, and notice those stubborn black specks creeping up the corners. It’s gross. If you have teenagers who take 45-minute showers and never turn on the exhaust fan, you already know this battle well. Mildew isn't just a cosmetic issue. It eats away at the porous cement holding your tiles together.

When you first spot that fuzzy green or black growth, don't just ignore it. Grab a dry microfiber cloth immediately. Wipe down the affected grout lines to remove surface moisture. Mildew thrives on dampness, so starving it of water is your first line of defense. Next, turn on your bathroom exhaust fan. I recommend letting a Broan NuTone fan run for at least 20 minutes to pull the ambient humidity out of the room. Open a window if the weather permits. Getting air moving across the tile surface stops the spores from spreading further while you gather your cleaning supplies.

What You'll Need (tools/products)

You can't just use any old sponge and expect miracles. In my experience cleaning tile for 10 years, using the right mechanical agitation and chemical combination is the only way to pull stains out of deep grout pores. This isn't the cheapest option, but investing in proper tools saves you hours of pointless scrubbing. Below is the exact kit I keep in my cleaning caddy for mildew removal.

Product/Tool	Purpose	Estimated Cost
RMR-86 Instant Mold Stain Remover	Heavy-duty chemical lifting for deep black stains	$18 - $22
Rubbermaid Reveal Grout Brush	Mechanical agitation with stiff 1/8-inch bristles	$8 - $12
OxiClean Versatile Stain Remover	Oxygen-based alternative for sensitive noses	$10 - $15
Pumice Stone (with handle)	Physical scraping for calcified mildew crusts	$6 - $9
N95 Respirator Mask	Lung protection from airborne spores and fumes	$15 - $25 (pack)

Step-by-Step Removal

I'll be honest, this takes elbow grease. There is no magic spray that works in ten seconds without some physical effort, especially if the mildew has been sitting there since the previous tenant moved out. Follow these steps exactly to restore your grout to its original color.

Step 1: Prep and Protect the Area

Put on your N95 mask and a pair of nitrile gloves. The spores you disturb will become airborne, and you don't want to breathe them in. Remove all shampoo bottles, loofahs, and razors from the shower caddy. You need unobstructed access to every single grout line. Lay down an old towel at the base of the tub to catch the chemical runoff and protect your drain finish from prolonged exposure to harsh cleaners.

Step 2: Apply the Chemical Cleaner

Spray the RMR-86 directly onto the dry grout lines. Don't wet the tiles first. The chemical needs to penetrate the porous cement, and if the grout is already saturated with water, the cleaner will just sit on the surface. Apply a generous, even coat until the lines look thoroughly soaked. Keep the spray nozzle about 6 to 8 inches away from the wall to ensure a wide, even distribution pattern.

Step 3: The Dwell Time (Crucial)

Walk away. Grab a coffee. I've found that letting the chemical dwell for exactly 12 to 15 minutes allows the active sodium hypochlorite ingredients to break down the fungal roots without evaporating too quickly. If you have a heavily neglected guest bathroom that hasn't seen a proper scrubbing in years, you might need to mist it a second time at the 10-minute mark to keep it wet. Do not let the solution dry on the tile.

Step 4: Mechanical Agitation

Grab your Rubbermaid Reveal Grout Brush. Scrub the grout lines with firm, circular motions until the foam turns gray or brown. The stiff bristles are specifically designed to reach into the microscopic valleys of sanded grout. The mildew lifts right up. Focus extra attention on the bottom corners where water naturally pools and stagnates.

Step 5: Rinse and Extract

Turn your showerhead to the highest pressure setting and rinse the walls with hot water (ideally around 120 degrees Fahrenheit). The heat helps dissolve any remaining chemical residue. Use a squeegee to pull the dirty water off the walls immediately. Finally, dry the grout lines with a clean microfiber towel to prevent new spores from settling into the damp pores.

Alternative Methods

Sometimes you can't use heavy-duty chlorine-based chemicals. Maybe you have a sensitive nose, or perhaps you're cleaning a small, unventilated powder room where the fumes would be overwhelming. Here are three backup methods I rely on when the situation calls for a different approach.

Method 1: The Oxygen Bleach Paste

Mix OxiClean powder with just enough warm water to form a thick, toothpaste-like consistency. Apply this paste directly to the stained grout using an old toothbrush. Let it sit for 30 to 45 minutes. Oxygen bleach releases ions that break down stain molecules without the harsh, toxic fumes of chlorine. It’s highly effective for organic stains, though it won't kill deep-rooted black mold as aggressively as RMR-86. Scrub vigorously and rinse thoroughly.

Method 2: High-Temperature Steam Cleaning

If you want to avoid chemicals entirely, steam is your best friend. I use the Dupray Neat Steam Cleaner, which heats water to 275°F at the boiler. Attach the grout brush nozzle and run the steam directly along the grout lines. The intense heat instantly kills mildew spores and blasts the dirt out of the pores. You'll need to wipe away the loosened grime with a microfiber cloth immediately, or it will just settle back into the wet grout as it cools.

Method 3: The Grout Pen Cover-Up

When your landlord inspects next week and you simply don't have time to scrub, a grout pen is a viable cosmetic fix. I recommend the Lanco Grout Pen for quick touch-ups. Clean the surface with rubbing alcohol first to remove any oils. Then, carefully trace the pen over the stained lines. This isn't a permanent cure, and it will peel if the underlying mildew isn't killed first, but it buys you a few months of visual relief.

Prevention Tips

Getting the mildew out is only half the battle. Keeping it from coming back requires a change in your daily bathroom habits. I preach these three rules to every single one of my residential clients.

• Squeegee After Every Shower: Keep an OXO Good Grips squeegee hanging in the shower. Taking 30 seconds to pull the water off the tiles removes the moisture that mildew needs to germinate. It’s a tiny habit that makes a massive difference.
• Seal Your Grout Annually: Unsealed grout is basically a sponge for dirty water. Once your grout is completely clean and dry for 48 hours, apply a coat of Miracle Sealants 511 Impregnator. This penetrating sealer fills the microscopic pores, creating a hydrophobic barrier that repels water and fungal spores.
• Manage the Humidity: Run your exhaust fan during your shower and leave it on for at least 20 minutes after you turn the water off. If your fan is weak or noisy, replace it. A modern, quiet fan like the Panasonic WhisperCeiling moves enough CFM to actually dry the room out.

FAQ

Will bleach ruin my grout?

Undiluted bleach can actually degrade the cementitious binders in your grout over time, causing it to crumble and crack. I recommend using oxygen bleach or specialized mildew removers instead for long-term maintenance. If you must use chlorine bleach, dilute it heavily and rinse thoroughly.

How often should I reseal my shower grout?

You should plan to reseal your shower grout every 12 to 18 months, depending on how heavily the bathroom gets used. I always test my grout by dropping a few beads of water on the surface; if it soaks in dark within three minutes, it's time to reseal. High-traffic family bathrooms might need annual attention.

Can I just paint over the mildew?

Painting directly over active mildew is a terrible idea because the fungal spores will continue to grow beneath the paint layer. The moisture trapped under the paint will cause it to bubble and peel within a few weeks. You must completely kill and remove the stain before applying any cosmetic grout colorant.

Is black mold in grout dangerous?

While most shower mildew is just unsightly Cladosporium, true black mold can release mycotoxins that trigger severe respiratory issues. I always advise wearing an N95 mask and gloves when scrubbing heavy black growths in poorly ventilated spaces. If you have asthma or immune deficiencies, hire a professional remediation service to handle it safely.